1. Field of the Invention
The present invention relates to a doctor blade, and, more particularly, to an apparatus for measuring doctor blade geometric deviations.
2. Description of the Related Art
Electrophotographic image forming devices, such as laser printers, include a drum having a rigid cylindrical surface that is coated along a defined length of its outer surface with a photoconductive material. The surface of the photoconductive drum is charged to a uniform electrical potential and then selectively exposed to light in a pattern corresponding to an original image. Those areas of the surface of the photoconductive drum exposed to light are discharged thus forming a latent electrostatic image on the photoconductive surface. A developer material, such as toner, having an electrical charge such that the toner is attracted to the photoconductive surface is brought into contact with the photoconductive surface.
The toner is stored in a toner reservoir adjacent to the photoconductive drum. A doctor blade and a developer roller are positioned between the toner reservoir and the photoconductive drum for controlling the amount of toner that is transferred to the photoconductive drum. Referring to FIGS. 1A and 1B, a doctor blade 10 may be, for example an elongate member having a longitudinal extent 12, for example, in the Z-axis direction, such that the longitudinal extent 12 would extend across the width of the developer roller. Adjacent a longitudinal edge 14 of doctor blade 10 there is formed a curved radial surface 16 having a radius 18, such that doctor blade 10 resembles a J-shape when viewed down the Z-axis as in the side view of FIG. 1B. Ideally, curved radial surface 16 is designed to contact the developer roller along a line of contact to meter the amount of toner transferred to the photoconductive drum. The ideal radius 18 may vary depending upon the application, but in one example is 700 microns.
It is important that the doctor blade make uniform and consistent contact across the entire length of the developer roller. Failure of the doctor blade to make uniform and consistent contact across the entire length of the developer roller will result in uneven toner amounts being transferred to the photoconductive drum, thereby resulting in inconsistent and unacceptable print quality.
Accordingly, it is highly desired that the doctor blade geometry be maintained within strict limits relating to linear straightness along the longitudinal extent 12 at the anticipated line of contact, and relating to the consistency of the radius 18 of the curved radial surface 16 along longitudinal extent 12 of doctor blade 10.
What is needed in the art is an apparatus for measuring doctor blade geometric deviations.